Question 226393 in Docker Question posted in
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Docker – How to prevent overwriting the whole environment field while using YAML anchors

I am writing my docker-compose.yml file and to avoid writing redundant lines especially for using different profiles for dev, uat, prod etc, I was using yaml anchors. Here is a sample for one of the adapters I used for uat and for dev.

Adapter:&Adapter
  image:"my-image"
  profiles:
    - uat
  environment:
    - JAVA_OPTS="${JAVA_OPTS} -Dloader.main=com.my.class"
    - SPRING_PROFILES_ACTIVE=uat
  volumes:
    - /local/path/to/logs:/logs
  depends_on:
    - some_image

Adapter-dev:
  <<: *Adapter
  profiles:
    - dev
  environment:
    - SPRING_PROFILES_ACTIVE=dev

.env file contains:

JAVA_OPTS=-Xmx3g -Xms3g

The key part is that the JAVA_OPTS is a must have in order to run properly. The JAVA_OPTS is stored in a .env file, and I append to the JAVA_OPTS variable to specify my main class. I just found out that doing it in the way above, it overwrites the environment entirely and only passes the SPRING_PROFILES_ACTIVE to my docker container’s environment variables. What I expected would be that only SPRING_PROFILES_ACTIVE would be overwritten, but the JAVA_OPTS would be preserved. How can I only overwrite the SPRING_PROFILES_ACTIVE in my docker-compose.yml without overwriting the JAVA_OPTS?

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2

Answers


  1. 0

    This might be a case where I’d use Compose’s support for multiple Compose files, which are able to combine per-service settings. Compose profiles are better for selecting which service to run, but not necessarily for controlling how to run it.

    You’d have a base docker-compose.yml file that listed all of the settings that were required in every environment

    # docker-compose.yml
version: '3.8'
services:
  adapter:
    image: "my-image"
    environment:
      - JAVA_OPTS="${JAVA_OPTS} -Dloader.main=com.my.class"
    volumes:
      - /local/path/to/logs:/logs
    depends_on:
      - some_image

    Then you’d have a file per environment that added settings for only that environment

    # docker-compose.uat.yaml
version: '3.8'
services:
  adapter:
    environment:
    - SPRING_PROFILES_ACTIVE=uat

    When you go to run docker-compose commands, you can then specify both files using docker-compose -f options. Note that you need to specify both files on every docker-compose invocation; setting a $COMPOSE_FILE environment variable may be a little easier.

    docker-compose -f docker-compose.yml -f docker-compose.uat.yaml up -d

    There are two versions of the Compose tooling, an older one that runs as a standalone tool and a newer one packaged as a docker CLI extension. This setup will work with both of them.

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  2. 0

    In Compose you can set up one service to extend another. This does essentially what you’re showing with YAML anchors, but it also lets you provide additional settings.

    version: '2.4'
services:
  adapter:
    image: "my-image"
    profiles: []
    environment:
      - JAVA_OPTS="${JAVA_OPTS} -Dloader.main=com.my.class"
    volumes:
      - /local/path/to/logs:/logs

  adapter-uat:
    extends:
      service: adapter
    profiles:
      - uat
    environment:
      - SPRING_PROFILES_ACTIVE=uat
    depends_on:
      - some_image

  adapter-dev:
    extends:
      service: adapter
    profiles:
      - dev
    environment:
      - SPRING_PROFILES_ACTIVE=dev
    depends_on:
      - some_image

    depends_on: is documented to not be reused in extends: services, so I’ve copied it into each per-environment service here.

    There are two versions of the Compose tool. If you are using the older version of the tool (docker-compose --version says it’s version 1) then be aware that the Compose file format version 3 doesn’t include extends:; you need to declare a version: 2.x at the start of the file and you will be unable to use some Swarm-related features in version 3 of the file format.

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